The present invention relates to a positive-working radiation-sensitive mixture which contains as essential constituents:
a) a compound which forms a strong acid on irradiation, PA1 b) a compound having at least one C--O--C or C--O--Si bond which can be cleaved by acid, and PA1 c) a water-insoluble binder which is soluble or at least swellable in aqueous alkaline solutions.
The invention also relates to a radiation-sensitive copying material produced from this mixture which is suitable for producing photoresists, electronic components, printing plates or for chemical milling.
In UV lithography, the limit of resolution is governed by the wavelength of the radiation used. The continuous miniaturization of the structural dimensions, for example, in chip production, therefore requires modified lithographic techniques in the submicron region. Owing to their short wavelength, high-energy UV light or electron beams and X-ray beams, for example, are used. This modification of the lithographic techniques changes the requirements imposed on the radiation-sensitive mixture. A summary of these requirements is given, for example, in the treatise by C. G. Willson entitled "Organic Resist Materials - Theory and Chemistry" (Introduction to Microlithography, Theory, Materials, and Processing, edited by L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219: 87 (1983), American Chemical Society, Washington). There is therefore an intensified requirement for radiation-sensitive mixtures which are preferably sensitive in a wide spectral range and can accordingly be used in conventional UV lithography or, without a loss in sensitivity, in advanced technologies such as, for example, mid-UV or deep-UV, electron or X-ray lithography.
Mixtures containing acid donors and acid-cleavable compounds are described, for example, in DE 2,306,248 (=U.S. Pat. No. 3,779,778) , 2,610,842 (=U.S. Pat. No. 4,101,323) , 2,718,254 (=U.S. Pat. No. 4,247,611) , 2,718,259 (=U.S. Pat. No. 4,189,323), 2,928,636 (=U.S. Pat. No. 4,311,782), 3,151,078 (=U.S. Pat. No. 4,506,006), 3,544,165 (=U.S. Pat. No. 4,786,577), 3,601,264, 3,730,783, 3,730,785 and 3,730,787, in EP 0,006,626 (=U.S. Pat. No. 4,250,247), 0,006,627 (=U.S. Pat. No. 4,248,957), 0,042,562 (=U.S. Pat. No. 4,506,003), 0,202,196 and 0,302,359, and also in U.S. Pat. Nos. 4,491,628 and 4,603,101. Upon irradiation of these materials, photolysis of the compound (a) forms an acid which brings about a cleavage of the C--O--C or C--O--Si bond of the compound (b) so that the irradiated regions of the photosensitive layers become soluble in an aqueous alkaline developer.
Compounds (a) are characterized as photolytic acid donors and include, in particular, onium salts such as diazonium, phosphonium, sulfonium and iodonium salts of non-nucleophilic acids, for example of HSbF.sub.6, HAsF.sub.6, or HPF.sub.6 (J. V. Crivello, Polym. Eng. Sci., 23:953 (1983)), halogen compounds (EP 0,232,972, DE 1,572,089 (=GB 1,163,324), DE 1,817,540 (=U.S. Pat. No. 3,615,455), DE 1,949,010 (=U.S. Pat. No. 3,686,084), DE 2,317,846 (=GB 1,381,471 and 1,381,472), U.S. 3,912,606), in particular trichloromethyl triazine derivatives (DE 1,298,414 (=GB 1,234,648), 2,243,621 (=GB 1,388,492), 2,306,248, 2,718,259, 3,333,450 (=ZA 84/7165) and 3,337,024 (=U.S. Pat. Nos. 4,619,998 and 4,696,888) and also U.S. Pat. Nos. 3,515,552, 3,536,489 and 3,615,630) or trichloromethyl oxadiazole derivatives (DE 2,851,472 (=U.S. Pat. Nos. 4,212,970 and 4,232,106), 2,949,396 (=U.S. Pat. No. 4,279,982), 3,021,590 (=U.S. Pat. No. 4,371,607), 3,021,599 (=U.S. Pat. No. 4,371,606) and DE 3,333,450), o-quinonediazidesulfochlorides or organometal/organohalogen combinations.
The use of such photolytic acid donors, however, involves certain disadvantages which drastically restrict their possible uses in various fields of application. For example, many of the onium salts are toxic. Their solubility in many solvents is inadequate, which results in a limitation of the choice of resist-coating solvents. If the onium salts are used, some undesirable foreign atoms are introduced which may result in processing troubles, in particular in microlithography. Furthermore, during the photolysis they form Bronstedt acids with very strong corrosive action which render the use of radiation-sensitive mixtures containing them unsatisfactory on sensitive substrates.
The halogen compounds and also the quinonediazide sulfonyl chlorides form hydrohalic acids with strong corrosive action. On certain substrates, such compounds have only a limited storage life. According to the teachings of DE 3,621,376 (=U.S. Pat. No. 4,840,867), this was improved in the past by introduction of an intermediate layer between substrate and radiation-sensitive layer containing compounds of the type (a), but this resulted in an undesirable increase in defects and a reduction in the process reproducibility. In addition, it was generally believed that compounds of the type (b) can be cleaved only by the acid types described above which have good mobility in the photosensitive layer.
Recent work by F. M. Houlihan et al., SPIE 920:67 (1988) has shown that, in addition to the above-mentioned acid donors, nitrobenzyl tosylates, which form sulfonic acids of low mobility on exposure to light, can be used in certain acid-labile resist formulations. The sensitivities achieved in such cases and the thermal stabilities of the photoresists have, however, proven inadequate.
Owing to the disadvantages cited there is therefore a need for further acid donors which act photolytically, which do not have the disadvantages described above as constituents of radiation-sensitive mixtures and which consequently have sufficient reactivity and acid strength to convert compounds of the type (b) into their cleavage products even with short exposure times.